The Characterization of Campylobacter jejuni Respiratory Oxidases and Reductases and their Role in Host Colonization
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Date
2009-02-16
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Abstract
Campylobacter jejuni is a foodborne human pathogen responsible for the gastroenteritis disease, campylobacteriosis. C. jejuni is a commensal microorganism in the digestive tract of birds and the majority of campylobacteriosis cases are linked to poultry products. Although the natural habitat of C. jejuni is the anaerobic ceca of birds, C. jejuni has long been considered a microaerophile and the requirement of oxygen is mandatory for growth. Surprisingly, the genome sequence of C. jejuni contains genes that should allow the bacterium to utilize anaerobic respiration. In order to characterize the respiratory chain, mutants were constructed in each of the following enzymes: nitrate reductase (napA::Cm), nitrite reductase (nrfA::Cm), SN oxide reductase (Cj0264c::Cm), cbb3-terminal oxidase (ccoN::Cm), bd-terminal oxidase (cydA::Cm), and fumarate reductase (frdA::Cm).
Both oxidase mutants grow on plates, but ccoN::Cm is extremely oxygen sensitive. C. jejuni is able to grow anaerobically utilizing nitrate, nitrite, DMSO and TMAO as alternative electron acceptors; mutants in each enzyme are deficient in growth on their respective substrates. Fumarate is not an alternative electron acceptor for C. jejuni. Compared to the wild type strain, frdA::Cm had an affected growth phenotype under microaerobic conditions; it was only able to utilize half of the TCA intermediates for biomass. Because both fumarate reductase and succinate dehydrogenase can interconvert fumarate and succinate, a mutant was constructed in the succinate dehydrogenase (sdhA::Cm). Both enzymes equally contribute to fumarate reductase activity; however, frdA::Cm had no succinate dehydrogenase activity and was unable to perform succinate-dependent respiration. It was concluded that the enzyme annotated as a fumarate reductase was the sole succinate dehydrogenase, which acts as a respiratory electron donor.
Wild type and mutant strains were assessed for their ability to colonize poultry. cydA::Cm and Cj0264c::Cm colonized similarly to wild type, while frdA::Cm, napA::Cm, and nrfA::Cm were significantly deficient in colonization ability. ccoN::Cm was completely unable to colonize the avian host. We concluded that oxygen is the most important respiratory acceptor to C. jejuni both in vitro and in vivo.
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Keywords
respiratory acceptors, Campylobacter, host colonization
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Degree
PhD
Discipline
Microbiology
